Abstract
Hydrogen has been used for the determination of the pulmonary capacity by VanSlyke and Binger, 1 who pointed out the danger of explosion and of poisoning with arsine. This procedure was replaced by oxygen dilution methods, particularly the Christie method, 3 which has been in use in this laboratory for the last 10 years. A recent report 2 has resulted in new interest in hydrogen, because of the ease and rapidity of analysis for this gas by thermal conductivity. A preliminary report is made at this time of a new method employing helium, because it has all the advantages and none of the dangers of the hydrogen method.
A closed spirometer system with a blower is used. Carbon dioxide is absorbed by soda-lime. An important precaution is the addition of a water bottle to replace water vapor lost in the soda-lime. Dead space is measured by the oxygen dilution method. Part of the mixture circulating in the respiratory system is shunted through a thermal conductivity cell∗ with precautions to assure complete saturation of the gas mixture with water vapor. A meter, which is connected to the cell, is calibrated for helium in air fully saturated with water vapor over a range of 0-14% and also for variation in oxygen concentration of the mixture from 18-23%. Seven hundred ml of 98.2% pure “Medical” helium is added from a graduated cylinder with a leveling bottle to 4,800 ml of air in the system. When this is mixed by the blower, the concentration is 12.5%. The meter reading is compared with the calibration curve to assure proper function of the indicating unit. Two hundred ml of oxygen are then introduced to approximate the concentration of air.
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